So roughly one to two years ago I heard that astronomers had discovered evidence that the far reaches of our observable universe were receeding from us (as expected), but were also beginning to accelerate! No one knew at the time what could possibly cause this, but measurement after measurement seemed to back it up. I haven’t heard anything about it since then, and am curious if any progress was ever made.
Why is our universe growing faster than it was yesterday? Whats speeding it up, and what is it speeding to?
This topic touches on something else I’ve wondered for a long time, but never managed to get an answer to. Looking out from the far edge of our universe do I see the otherside? Is it cyclical, like a large globe? Is there a defined edge, an uncrossable event horizon, or is it infinite (somehow?)?
This has become known as dark energy. It was actually discovered in 1998.
Here’s a long article from Physicsworld that gives a good summary, and one much more readable than Wiki. You should be able to search on dark energy and get many more sources. You may not have noticed but there’s probably been an article in every issue of every science magazine for the last decade, not to mention zillions of websites and dozens of books. Dark energy: it’s everywhere!
There is no defined edge and current theories do not allow us to see back around to the beginning point. Even if the universe were curved that way, the expansion of the universe over its lifetime means that the farthest points are now unseeable by us because even traveling at the speed of light they would not reach us in the current age of the universe.
Whether the universe is infinite or merely huge but finite is a matter of intense debate.
>Looking out from the far edge of our universe do I see the otherside? Is it cyclical, like a large globe? Is there a defined edge, an uncrossable event horizon, or is it infinite (somehow?)?
I’m degreed in Astronomy but years behind the times. For what it’s worth:
The universe contains galaxies full of stars and other objects, and these galaxies are often in clusters. There are clusters of clusters. On a larger scale, the universe has a foamy texture, like soap suds. The bubbles in the suds are large voids that are much emptier, and the walls of the bubbles are sheetlike areas where galaxy clusters are more frequent, and the intersections where bubble walls meet represent the busiest areas, where there are many clusters of clusters of galaxies. On a scale larger than this foamy texture, the universe is uniform and featureless.
Apparently, about 13 or so billion years ago, the universe, and the room it occupies, sort of blew up out of nothing. I’m a little hazy on the following, but believe the foamy texture of the present universe is thought to come from quantum-physical fluctuations in the density of the earliest stages of the universe. There was an inflation period early in the universe’s history that froze these fluctuations into density variation on the largest known scale of structure in the universe. However - and thus the haziness - I think I just read something about superlarge black holes with high energy jets streaming out of them apparently sweeping clean large regions of space, which are the bubbles in the foam. So I’m confused whether the bubbles are frozen early quantum fluctuations or areas swept by supersized black holes and their jets.
In my understanding, it’s been known for some time now that the universe is infinite in size. That is, to say the least, at any speed you want to travel, you could go in a straight line and never run out of stuff to see.
General relativity does some funny things to what we can say about the universe for several reasons. It is expanding everyplace, so that on the scale of the foam and larger scales, any two objects you pick are moving apart from one another. This means that at some distance objects would be moving apart at the limiting velocity of “c”, and there are no objects further apart from that. Thus it means different things to think about what the distant universe is like right now, versus when it emitted whatever light we see from it. In fact there are even multiple versions of what “right now” should mean when discussing distant objects.
There is an edge to the universe only in limited senses. In one sense, the time it takes us to see the most distant objects is almost equal to the time that has elapsed since the initial blossoming of the universe. We refer to the edge of the “observable universe” when we talk about places that, when they emitted the energy we see today, were just barely starting to glow visibly, or were emitting the radiant energy associated with the “Big Bang” which we now see as the cosmic microwave background.
Here we go - the Real Universe is actually an 11-dimensional place. There are 9-dimensional objects floating around in it, and if they touch each other, they annihilate into 7 dimensional objects. More generally, objects floating in n-dimensional space and having (n-2) dimensions always have the possibility of finding and annihilating each other into (n-4) dimensional objects. Our 3D universe appears to be one of these, 3 dimensional, having gone through 4 annihilations. There are also 1-dimensional objects in our universe, called Strings.
So, here I have laid out what’s guaranteed to be interesting but maybe 30% wrong and 20% confused, for whatever it’s worth. And if there’s anything about heat transfer or nonlinear fitting I can help with, it’d be much less wrong.
Somebody, please come mop up after me, if you can!
The part of the universe that we can see LOOKS flat, so if it curves back around on itself the curve is very gentle and hence the universe must be very big. But we can’t say for sure right now if its infinite or not.
This is incorrect. Relativity limits the speed that objects can move through space, but it does not limit the speed at which space itself can stretch.
Imagine that space is expanding at a unform rate everywhere at once. Suppose a star that’s 1 lightyear from us is moving away from us at a speed of 1 meter per second. The a star that’s 2 lightyears away is moving at a speed of 2 meters per second. 3 lightyears, 3 meters per second, and so on. Then a star that is 300 million lightyears from us is receding from us at greater than the speed of light. This is possible because the star isn’t actually moving. Space is stretching around it.
In your post you actually allude to this sort of thing when you mention the inflationary period early in the life of the universe. During that time space was stretching much faster than it is now, so some parts of the universe moved away from each other at greater than light speed for a while, then slowed down so they could see each other again.
**Exapno ** links to a good article. The very, very short answer is: We don’t know why the expansion of the universe is speeding up. The term “dark energy” is a placeholder. It just means “whatever weird thing is making the expansion of the universe speed up”.
It’s not expanding into anything. Think of the surface of an inflating ballon with some dots drawn on it. As the balloon gets bigger, the dots move further apart. But there’s no edge to the surface. You can move any direction along the surface and there’s still more balloon ahead of you.